Non-woven depth filter cartridge

ABSTRACT

A new non-woven depth filter cartridge is formed by insertion of a core into filter mass formed in a continuous process. A mass of very fine diameter polymer filaments is overlaid by mass of larger diameter polymer filaments. The filaments are continuously accumulated on a spinning mandrel and advanced along and off of the mandrel by a press roller. An inner cylindrical surface of the cumulative filament mass forming the depth filter element is calendered, which facilitates insertion of a core member.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority from U.S. patent applicationSer. No. 09/296,070, filed on Apr. 21, 1999, for “Non-Woven Depth FilterElement” by Thomas M. Aune, et al., now pending; and U.S. patentapplication Ser. No. 09/550,814, filed on Apr. 18, 2000 for “Method ofProducing a Non-Woven Depth Filter Element” by Thomas M. Aune, et al.,now pending.

BACKGROUND OF THE INVENTION

[0002] The present invention relates to the field of fluid filtration,and in particular to depth filters. Specifically, the present inventionrelates to depth filters formed from non-woven melt-blown polymericfibers.

[0003] Non-woven melt-blown depth filters are well known and are widelyused in fluid filtration applications. Such filters can be formed byextruding softened polymeric materials through an orifice of a nozzle ina stream. Jets of gas (usually air) attenuate the polymer stream to formthe fibers, which are directed toward and collected by a rotatingmandrel. Fibers continue to build up on the rotating mandrel until atubular mass of fibers of the desired size and morphology is achieved.

[0004] Depth filters of the type described may include a core member tosupport the fiber mass. Depth filters of this type are typicallyproduced by placing a tubular core member over the mandrel and applyingthe polymer fibers directly on the core member. This process, however,is discontinuous and requires that a core member be replaced on themandrel after each depth filter is formed.

[0005] A continuous process for producing a coreless depth filter isalso known. According to this process, a coarse core layer of relativelylarge diameter polymer fibers are initially applied directly onto aspinning mandrel to form an inner cylindrical fiber mass. Finer polymerfibers are applied over the inner cylindrical mass to form the depthfilter element. The fiber mass forming the depth filter element iscontinuously advanced along and off of the mandrel by a press rollerlocated adjacent to the mandrel. The inner fiber mass of such a corelessdepth filter provides sufficient structural integrity to support anouter mass of relatively fine polymer fibers and withstand the fluidpressures to which the depth filter is subjected. The outer fiber massof the finer polymer fibers, on the other hand, comprises the filtrationzone of the depth filter.

[0006] Under some circumstances, it is desirable that depth filters becapable of filtering very fine particles (e.g., 1 micron) while allowingfluid under pressure to flow through the filter with a minimum drop inpressure. Depth filters with an initial pressure drop in the range of3-4 p.s.i.d. per gallon per minute of liquid flow per ten inch elementare known.

[0007] There continues to be a need in the art for a method ofcontinuously producing a depth filter element for use with a core memberwhich yields a suitable depth filter capable of filtering particles 1micron or less with a minimum pressure drop.

BRIEF SUMMARY OF THE INVENTION

[0008] The present invention is directed to a composite polymer filamentmass especially suitable for use in constructing a cylindrical depthfilter element. In the preferred embodiment, the composite polymerfilament mass is comprised of a first cylindrical mass of very smalldiameter polymer filaments, i.e., diameters of less than about 1.5microns. An inner cylindrical portion of the first cylindrical massdefines a smooth inner cylindrical surface of the composite filamentmass. The first cylindrical mass of filaments is surrounded by a secondcylindrical mass of polymer filaments having diameters greater than 1.5microns.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009]FIG. 1 is a schematic diagram generally illustrating an apparatusfor continuously producing a non-woven depth filter element.

[0010]FIG. 2 is a schematic diagram illustrating the apparatusconfiguration for continuously producing a depth filter element of thepresent invention.

[0011]FIG. 2A is an enlarged view of the collection device of theapparatus of FIG. 2.

[0012]FIG. 3 is a cross-sectional view of a depth filter element of thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] The present invention relates to an improved non-woven depthfilter element as well as an apparatus and a method for continuouslymaking such element. Throughout the specification, the term “coreless”is used to describe certain depth filter elements. Unless otherwiseindicated, the term “coreless” refers to a filter element which is notprovided with a separate support core member.

[0014] Reference is first made to FIG. 1 to generally illustrate anapparatus which is used to continuously manufacture a depth filterelement of indefinite length in which the depth filter is comprised ofat least two discrete sets of continuous filament material of differentdiameters or of different materials. One such apparatus suitable for thepresent invention is disclosed in U.S. Pat. No. 5,340,479, which isfully incorporated herein by reference. The preferred embodiment of theapparatus includes a motor driven screw type extruder 10 which issupplied with thermoplastic polymeric material from a source (notshown). The particular thermoplastic polymeric material may be any oneof a variety of synthetic resinous materials which can produce thefilaments used in manufacturing the depth filter element of the presentinvention. Although the class of polymeric materials known aspolypropylenes are preferred, polyesters, Nylon, polyurethanes and othermaterials may be used as well.

[0015] Within the extruder 10, the polymeric material is heated to amolten state, at which time it is metered and conveyed into a heateddelivery line 11. The material is maintained or further heated in theline 11 and is ultimately fed into a common manifold 12. The heatedmolten polymeric material is then directed by the manifold 12 tofilament forming means, which in one embodiment is in the form of twofilament delivery systems 14 and 16. Each of the delivery systems 14 and16 is substantially identical and functions to produce one or moresubstantially continuous polymeric filaments and to direct the samealong a predetermined path toward a collection means as will bedescribed in greater detail below.

[0016] The filament delivery system 14 includes a motor driven gear typepositive displacement metering pump 18 which receives molten polymericmaterial from the manifold 12 and pumps it to heater block 24. The speedof the motor 19 which drives the metering pump 18, and thus the rate atwhich the material is metered through the pump 18 is electronicallycontrolled by an appropriate control means 20.

[0017] Heater block 24, which is independently heated via heating means(not shown) is provided with internal passages which lead to a pluralityof nozzles 25. The heating means, and thus the temperature of thepolymeric material within heater block 24, is controlled by temperaturecontrol 26. Each nozzle 25 includes an orifice, the size of which may beselected as desired to assist in achieving a desired filament size ordiameter. The molten material fed to each nozzle 25 exits the orifice ina stream.

[0018] Associated with each nozzle 25 are attenuating mechanisms 28,which comprise a plurality of gas or air jets. Gas flowing out of theattenuating mechanisms 28 function to attenuate the stream of moltenmaterial exiting from the nozzles 25 to form polymeric filaments in amanner known in the art. The attenuating mechanisms 28 accordingly maybe of any design known in the art including that described in U.S. Pat.No. 4,173,443, the disclosure of which is incorporated herein byreference.

[0019] Each of the attenuating mechanisms 28 is associated with a gasheater 29 and gas supply source 31. Gas supply source 31 provides gasvia conduit 32 and appropriate valves and regulators to the heater 29where its temperature is elevated or lowered to the desired temperaturevia the temperature control 30. The gas is then fed from the heater 29through conduit 34 to the attenuating mechanisms 28. Attenuatingmechanisms 28 may be provided with gas from a common supply source,heater and temperature control, or alternatively, separately controlledgas sources may be employed for each attenuating mechanism 28.

[0020] The filament delivery system 16 is substantially identical tothat of the system 14 described above. Specifically, the system 16includes a heater block 38, an independently driven positivedisplacement metering pump 36, and motor 39 and motor elements 40.Heater block 38 is provided with a plurality of nozzles 42 andtemperature control 41. The system 16 is also provided with a pluralityof attenuating mechanisms 44 associated with the nozzles 42. Pressurizedgas is passed to each attenuating mechanisms 44 from a gas supply source45 via conduit 46, a heater 48 and conduit 49. Temperature control 50regulates and controls the temperature produced by heater 48. Theprovision of separate filament delivery systems 14 and 16 enablesseparate control and production of polymeric filaments produced by eachsystem 14 and 16.

[0021] Each of the delivery systems 14 and 16 is capable of producing aplurality of discrete, continuous filaments 51 and 52 respectively whichare directed from the orifices 25 and 42 and attenuating mechanisms 28and 44, respectively, toward a filament collection device 54 illustratedin FIG. 1. The filament collection device 54 includes a central,rotatable mandrel 55 which extends from a drive motor 58. Adjacent tothe mandrel 55 and spaced therefrom is a press roll member 56 rotatableabout the axis 57. During operation, the plurality of filaments 51 and52 are directed in a flared pattern toward the rotating mandrel 55 andcollected thereon in a manner known in the art. The rotating pressroller 56 engages the filaments which have accumulated on the rotatingmandrel 55. As sufficient filaments are built up on the mandrel 55, thepress roller 56 forces the filament mass 59 off the axial end of themandrel 55 in the direction of the arrow 53 to produce a continuousfilament mass 59 of indefinite length. The entire filament collectiondevice 54 is known to those skilled in the art and may be similar tothat described in U.S. Pat. No. 4,240,864, the disclosure of which isincorporated herein by reference.

[0022] The apparatus of FIG. 1 has been demonstrated to be adequate forproducing coreless depth filters in which filament delivery system 14 isconfigured to produce polymeric filaments having relatively largediameters (i.e., greater than 15 microns), and filament delivery system16 is configured to produce polymeric filaments having smaller diameters(i.e., 1-15 microns). A depth filter element produced thereby has atubular configuration with an innermost cylindrical zone of relativelylarge polymeric filaments which defines a support for an outercylindrical zone of the smaller polymeric filaments which form afiltration zone of the depth filter. The present invention, however, isdirected to an novel apparatus configuration and method for continuouslyproducing an improved depth filter for use with a core member.

[0023] The improved depth filter of the present invention is generallycharacterized by an inner cylindrical mass of very small diameterpolymeric filaments (i.e., 0.5-1.5 microns), a calendered (i.e. smooth)inner cylindrical surface and an outer cylindrical mass of coarser,large diameter polymeric filaments (i.e., 4-10 microns or greater).While cored depth filters having a filtration zone near the core areknown in the art, production of such filters is discontinuous andrequires that the relatively fine polymeric filaments comprising thefiltration zone to be deposited directly on a core member supported by amandrel. The improved apparatus configuration and process of the presentinvention overcomes the limitations of such a discontinuous depth filterproduction process by enabling a continuous process whereby very smalldiameter polymeric filaments (0.5-1.5 microns) are directly applied toand collected on a mandrel of a filament collection device, such asfilament collection device 54 shown in FIG. 1, with larger diameterpolymeric filaments thereafter applied over the small filament mass. Acalendered inner cylindrical surface of the depth filter, comprised of aportion of the mass of very small polymeric filaments, results from thisprocess, which allows for an easy, post-production insertion of a coremember known in the art. The process of the present invention thereforeenables a continuous production of a depth filter element independent ofa core member to be used with the depth filter.

[0024] For a more complete understanding of the present invention,reference is made to FIG. 2, which is a schematic diagram illustratingthe apparatus of FIG. 1 configured for continuously producing a depthfilter element of the present invention. As shown in FIG. 2, fourfilament producing devices 100, 102, 104, and 106 are employed, each ofwhich comprises a nozzle and an attenuating mechanism, such as nozzle 25and attenuating mechanism 28 of FIG. 1. Filament producing devices 100,102, 104, and 106 are longitudinally aligned along a common axis 108which is parallel with mandrel 110. The nozzle of each filamentproducing device 100, 102, 104, and 106 includes an orifice whichdefines an axis 112 that is perpendicular to axis 108 and mandrel 110.Axis 112 generally corresponds to the flow axis of molten polymerexiting the nozzle orifice. In one preferred embodiment, filamentproducing devices 100, 102, 104, 106 are located approximately 30 inchesfrom mandrel 110. As depicted, the attenuating mechanism of filamentproducing device 100 is oriented to produce gas streams which aregenerally aligned and parallel with axis 112. This orientation resultsin a flared filament pattern 114 being directed toward mandrel 110.

[0025] Filament pattern 114 is comprised of polymer filaments havingvery small diameters of between about 0.5 micron to about 1.5 microns.As a non-limiting example, polymer filaments of filament pattern 114were produced in the depth filter of the instant invention by passingpolypropylene heated to a temperature of 420° C. to about 425° C.through a nozzle having an orifice size of about 0.011 inch at a rate ofabout 3.8 pounds per hour and passing a heated gas at a temperature of400° C. at a rate of 11 cubic feet per minute over the molten polymerstream exiting the nozzle orifice. It will be appreciated that a personskilled in the art can readily determine other parameter combinationssuitable to form very fine filaments of between about 0.5 microns toabout 1.5 microns, and that the parameters necessary to form such veryfine filaments will vary according to the particular polymer materialused.

[0026] The attenuating mechanism of filament producing device 102,however, is oriented to produce gas streams which are directed at anangle, relative to axis 112 of device 102, away from filament pattern114. By orienting the attenuating mechanism of device 102 in thismanner, a flared filament pattern 116 is produced which substantiallyavoids overlapping with filament pattern 114. The objective of thisconfiguration is to allow polymeric filaments from device 100 toaccumulate and form a mass on mandrel 110 with minimal mixing ofpolymeric filaments from device 102. In one preferred embodiment, theattenuating mechanism of device 102 is oriented to produce gas streamsaway from filament pattern 114 at an angle of between about 30° to about40° relative to axis 112 of device 102. In the depth filter of thepresent invention, the polymer filaments of filament pattern 116 havediameters of between about 4 microns to about 8 microns. By way of anon-limiting example, the filaments of pattern 116 were produced bypassing polypropylene heated to a temperature of 420° C. to about 425°C. through a nozzle having an orifice size of about 0.011 inch at a rateof about 3.8 pounds per hour and passing a gas at ambient temperature ata rate of 11 cubic feet per minute over the molten polymer streamexiting the nozzle orifice.

[0027] With respect to device 104, the attenuating mechanism is orientedto produce gas streams at an angle directed toward filament pattern 116to produce a filament pattern 118 which substantially overlaps withfilament pattern 116. In one preferred embodiment, the attenuatingmechanism of device 104 is oriented to produce gas streams at an angleof between about 5° to about 10° relative to axis 112 of device 104. Inthe depth filter of the present invention, the polymer filaments offilament pattern 118 have diameters of between about 6 microns to about10 microns. By way of a non-limiting example, the filaments of pattern118 were produced by passing polypropylene heated to a temperature of390° C. through a nozzle having an orifice size of about 0.011 inch at arate of about 5.1 pounds per hour and passing a gas at ambienttemperature at a rate of 11 cubic feet per minute over the moltenpolymer stream exiting the nozzle orifice.

[0028] The attenuating mechanism of device 106 is oriented to produce agas stream angled toward filament pattern 118. In a preferredembodiment, this orientation results in a gas stream directed at anangle of between about 10° to about 20° relative to axis 112 of device106. In the described configuration, device 106 produces filamentpattern 120, which substantially overlaps filament pattern 118. In thedepth filter of the present invention, the polymer filaments of filamentpattern 120 have diameters of between about 6 microns to about 10microns. By way of a non-limiting example, the filaments of pattern 120were produced by passing polypropylene heated to a temperature of about390° C. through a nozzle having an orifice size of about 0.016 inch at arate of about 5.1 pounds per hour and passing a gas at ambienttemperature at a rate of 16 cubic feet per minute over the moltenpolymer stream exiting the nozzle orifice.

[0029] As further shown in FIG. 2, filament producing device 100 isoriented such that filament pattern 114 is generally centered on nip 122of press roller 124. In one embodiment, filament pattern 114 has a widthof about 6 to 8 inches at mandrel 110. Filament pattern 116 is intendedto be substantially separate from filament pattern 114, with sufficientoverlap or intermingling of each pattern, however, to prevent separationor delamination of the filament mass formed. Filament pattern 114therefore accumulates on mandrel 110 as a generally homogenous filtermass. Filament patterns 116, 118 and 120 are intended to substantiallyoverlap, which results in a relatively heterogenous filament mass beingapplied over the filament mass produced by filament pattern 114.

[0030] As more completely shown in FIG. 2A, which is an enlarged view ofthe collection device of FIG. 2, an accumulated mass of filaments 114 aand 114 b from filament pattern 114 are produced on opposite sides ofnip 122 of press roller 124. In one embodiment, press roller 124 isoriented at an angle relative to mandrel 110 with nip 122 in contactwith mandrel 110. As a non-limiting example, outer surface 123 of pressroller 124 is angularly displaced by about 3° relative to mandrel 110.So configured, sufficient filaments from filament pattern 116 areintermixed with those of filament mass 114 b that the filament mass 114a is drawn past nip 122 as the collective filament mass 126 is movedalong mandrel 110 in the direction indicated by arrow 128. As thefilaments from filament mass 114 a are drawn past nip 122, they arecompressed between nip 122 and mandrel 110 to form a dense layer of thevery small diameter filaments produced in filament pattern 114. Becauseof the small diameter of these filaments, the filaments are able tosufficiently cool in the time it takes for them to accumulate and passby nip 122. As a result, no cross-welding of filaments results asfilament mass 114 a is compressed by nip 122. Furthermore, because ofthe angular placement of press roller 124, compression of filaments incollective filament mass 126 varies along the length of press roller124. This results in a filament mass having a varying density gradient,with the filament density of filament pattern 114 being generallygreater than that of the filament mass comprised of filament patterns116, 118 and 120. A filament mass of the present invention may be formedin any desirable lengths and subsequently cut to any desirable size toform discrete depth filter elements.

[0031] It was originally believed that very fine polymer filaments ofless than 1.5 microns could not be successfully applied to a collectionmechanism employing a spinning mandrel and press roller without ropingof the filaments or sticking to the mandrel. It was also not expectedthat a smooth calendered inner cylindrical surface would result to afilament mass produced from the method of the present invention. Rather,it was anticipated that a continuous process as described would producea surface defined by fine, fuzzy filaments, which could hamper insertionof a core member. The method of the present invention, however,demonstrates a way of continuously producing at an advantageous rate afilament mass suitable for making a depth filter element having an innerfiltration zone comprised of very fine filaments and an outer filtrationzone comprised of larger filaments, and which produces a smooth innercylindrical surface that allows for subsequent easy insertion of a coremember.

[0032]FIG. 3 illustrates a cross-sectional view of the filament mass 126produced by the present invention. As generally depicted, filament mass126 is comprised of an inner cylindrical calendered layer 130, which iscontiguous with an inner filtration zone 132 comprised of a relativelyhomogenous zone of very fine polymer filaments have diameters of lessthan about 1.5 microns, and generally in a range of between about 0.5micron and 1.5 microns. Calendered layer 130 results from thecompression of filaments having the same morphology and size as thosefound in filtration zone 132. In one embodiment, calendered layer has athickness of about 5 mils which defines a smooth inner cylindricalsurface 134 of filament mass 126. Filament mass 126 is further comprisedof an outer filtration zone 136 formed by a heterogenous filament masshaving intermixed filaments having diameters ranging in size from about4 microns to about 10 microns. In one embodiment, filament mass 126 hasa mass of 110 grams per ten inch section.

[0033] Depth filter elements formed in the manner described relative toFIGS. 1, 2 and 2A and having the characteristics described relative toFIG. 3 have demonstrated excellent particle filtration and fluidthroughput capabilities. For example, the depth filter of the presentinvention has demonstrated to be 99.9% effective at removing 1 micronparticles. Furthermore, the depth filter element of the presentinvention allows fluid throughput with a minimal drop in fluid pressureacross the filter (e.g. pressure drops of about 1.5 p.s.i.d. per gallonper minute of liquid flow per ten inch element).

[0034] Although the description of the preferred embodiment and methodhas been quite specific, it is contemplated that various modificationscould be made without deviating from the spirit of the presentinvention. Accordingly, it is intended that the scope of the presentinvention be dictated by the appended claims rather than by thedescription of the preferred embodiment.

What is claimed is:
 1. A non-woven filter cartridge comprising: acylindrical core member; a first cylindrical mass of essentiallycontinuous, intertwined, and thermally bonded polymer filaments adjacentto the core member, the polymer filaments of the first mass havingdiameters of less than about 1.5 microns; a second cylindrical mass ofessentially continuous, intertwined, and thermally bonded polymerfilaments adjacent to the first mass of polymer filaments, the polymerfilaments of the second mass having diameters greater than about 1.5microns; wherein the filter cartridge has an efficiency in removing 1micron particles greater than or equal to at least about 99.9%, andwherein a pressure drop across the filter cartridge is less than about 3pounds per square inch for every gallon per minute of flow through a 10inch long section of the filter cartridge.
 2. The non-woven filtercartridge of claim 1 wherein the filaments of the first mass havediameters less than about 1 micron.
 3. The non-woven filter cartridge ofclaim 1 wherein the filaments of the second mass have diameters rangingfrom about 4 microns to about 10 microns.
 4. The non-woven filtercartridge of claim 1 wherein the pressure drop across the filtercartridge is about 1.5 pounds per square inch for every gallon perminute of flow through the 10 inch section of the filter cartridge. 5.The non-woven filter cartridge of claim 1 wherein the first mass ofpolymer filaments comprises a first filament zone and a second filamentzone, the first filament zone defining a calendered layer having adensity of filaments which is substantially greater than that of thesecond filament zone.
 6. The non-woven filter cartridge of claim 5wherein the first filament zone is adjacent to the core.
 7. Thenon-woven filter cartridge of claim 6 wherein the calendered layer has athickness of about 5 mils.
 8. The non-woven filter cartridge of claim 7wherein the second filament zone and the second cylindrical mass areeach substantially thicker than about 5 mils.
 9. The non-woven filtercartridge of claim 1 further comprising: a transition region includingfilaments from the first mass intertwined with filaments from the secondmass.
 10. The non-woven filter cartridge of claim 1 including a densitygradient between the first filament mass and the second filament mass.11. A non-woven filter cartridge comprising: a cylindrical core member;a first cylindrical mass of essentially continuous, intertwined, andthermally bonded polymer filaments positioned over the core member, thefirst mass of polymer filaments comprised of filaments having a diameterof less than about 1.5 microns, wherein a portion of the first mass ofpolymer filaments forms a calendered layer positioned adjacent the coremember; and a second cylindrical mass of essentially continuous,intertwined, and thermally bonded polymer filaments disposed over thefirst mass of polymer filaments, at least some of the polymer filamentsin the second mass being intertwined with some of the polymer filamentsin the first mass, the second mass of polymer filaments comprised offilaments having a diameter of greater than about 1.5 microns; whereinthe filter cartridge has an efficiency in removing 1 micron particles ofat least about 99.9% and wherein a pressure drop across the cartridge isless than about 3 pounds per square inch per gallon per minute of fluidflowing through a 10 inch long section of the filter cartridge.
 12. Thenon-woven cartridge of claim 11 wherein the filaments of the first masshave diameters of between about 0.5 microns and about 1 micron.
 13. Thenon-woven filter cartridge of claim 11 wherein the filaments of thesecond mass have diameters ranging from about 4 microns to about 10microns.
 14. The non-woven filter cartridge of claim 11 wherein thefilaments of the second mass have diameters larger than the diameters ofthe filaments of the first mass.
 15. The non-woven filter cartridge ofclaim 11 wherein the calendered layer has a thickness of about 5 mils.16. The non-woven filter cartridge of claim 15 wherein the secondcylindrical mass is substantially thicker than about 5 mils.